Fuel cells are electrochemical cells in which a free energy change resulting from a fuel oxidation reaction is converted into electrical energy. In an organic/air fuel cell an organic material such as methanol or other suitable fuel is oxidised to carbon dioxide at the anode whilst oxygen from air, or oxygen enriched air, or oxygen gas itself, is reduced to water at the cathode.
Two types of organic/air fuel cells are generally known:    1. An indirect fuel cell in which the organic fuel is catalytically reformed and processed into hydrogen, which is used as the actual fuel for the fuel cell by being oxidised at the anode.    2. A direct oxidation fuel cell in which the organic fuel is directly fed into the fuel cell and oxidised at the anode which typically employs platinum group metals or alloys containing platinum group metal as the catalyst.
Direct oxidation fuel cells are currently the subject of substantial interest for use in a wide variety of applications. Such cells have the potential for providing useful energy outputs in a “clean” and efficient manner using renewable fuels such as methanol. Such fuels can be obtained, for example, by biomass fermentation processes.
Difficulties encountered in producing a practical direct fuel cell include:                Catalyst and electrode design and efficiency, avoiding poisoning and minimising the production of undesirable side products such as carbon monoxide;        Efficiency of the cathode, especially if air is used as the oxygen containing gas, the nitrogen present can ‘blanket’ or slow down the transport of the oxygen to the catalyst surface;        Fuel ‘cross-over’, i.e. the anode and cathode of the cell are separated by an ionically conductive medium such as a high molecular weight electrolyte or solid proton conducting membrane, but if the fuel can permeate that membrane and be transported from the anode to the cathode then efficiency is lost; and        Choice of electrolyte—direct oxidation fuel cells often employ sulphuric acid as the electrolyte but the consequent presence of sulphate ions and sulphur can result in poor performance.        
In U.S. Pat. No. 5,599,638 an improved type of cell using a solid polymer electrolyte and improved electrodes is described, with yet further improvements being revealed in U.S. Pat. No. 6,303,244 by the same inventors. A notable feature of that work is the use of a solid polymer electrolyte, a perfluorosulphonic acid containing polymer, such as “Nafion®”. This avoids the use of sulphuric acid electrolyte and gives improved performance from the cell.
In U.S. Pat. No. 5,094,927 an alternative solid electrolyte is described, a proton conducting solid comprising at least one oxide of an element selected from Group IVB, VB, VEB, and VIII elements of the Periodic Table, silicon dioxide, and at least one fluoride of an element selected from the elements in Group IIA and IIIB of the Periodic Table. Such an electrolyte is proposed as a feature of an indirect (hydrogen/oxygen) fuel cell in that patent.
A disadvantage of the known types of fuel cell is that they generally require highly purified fuel to prevent catalyst poisoning. The fuel cell of U.S. Pat. No. 6,303,244 requires highly pure methanol, the inventors envisage having to fit filtration systems to remove hydrocarbon traces from the fuel when their invention is used in an automotive environment.
An object of the present invention is to provide improvements in or relating to fuel cells, whereby the aforesaid disadvantages of the prior art are obviated or mitigated.
A further object of the invention is to provide a direct oxidation type of liquid feed fuel cell that utilises photo-catalysed oxidation at the anode.
Another object of the invention is to provide means of gathering and directing light to the photocatalytic anode.
A yet further object of the invention is to provide a photocatalytic reactor that can be utilised in the intended destruction of organic compounds present in waste streams from industrial processes in an energy efficient manner.